The present disclosure generally relates to a paper treatment method that improves the wetting and adhesion properties of materials to an oil contaminated print. By subjecting the contaminated surface to the combined action of ultraviolet (UV) radiation and ozone, the UV radiation and ozone exposure can change the surface chemistry of the contaminated print allowing for favourable material—paper interactions leading to improved adhesion.
In conventional xerography, electrostatic latent images are formed on a xerographic surface by uniformly charging a charge retentive surface, such as a photoreceptor. The charged area is then selectively dissipated in a pattern of activating radiation corresponding to the original image. The latent charge pattern remaining on the surface corresponds to the area not exposed by radiation. Next, the latent charge pattern is visualized by passing the photoreceptor by one or more developer housings comprising thermoplastic toner, which adheres to the charge pattern by electrostatic attraction. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate, such as paper, to which it is fixed by a suitable fusing technique involving the application of heat, resulting in a xerographic print or toner-based print.
To ensure and maintain good release properties of the fuser roll, it has become customary to apply release agents to the fuser roll during the fusing process. These materials are applied as thin films of low surface energy liquids, for example, nonfunctional silicone oils or mercapto- or amino-functional silicone oils, to prevent toner offset.
U.S. Pat. No. 4,029,827 discloses the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. No. 4,101,686 and U.S. Pat. No. 4,185,140 disclose polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether, or mercapto groups. U.S. Pat. No. 5,157,445 discloses toner release oil having a functional organopolysiloxane.
The mechanism involved in the use of thin liquid films of fuser oils in two roll fuser systems to ensure release between the fuser roll surface and the thermoplastic toner is a dynamic cohesive failure or film splitting of the release oil in the diverging roll nip exit, leaving a barrier of fuser oil on both roll and the toner image surfaces. The residual film of release oil on the fused toner image and paper, which is referred to in this document as contaminating oil or oil contamination can cause problems with subsequent, end-use applications involving wetting or adhesion. After printing, images may experience a number of process treatments involving wetting and adhesion, including coating (as in overprint varnish application), lamination, application of adhesives (book-binding, post-it notes), thermal transfer printing (cheque post-encoding or bar code printing for example). Residual fuser oil present on the print image surface, typically as a discontinuous film, results in a complex surface energy gradient varying between low surface energy oil regions and relatively high surface energy toner and paper regions. Attempts to wet and adhere materials across this gradient results in numerous well-known surface tension related coating defects including pinholes, craters and reticulation for coating liquids and subsequent dried films; failure to achieve fiber tear when adhesive is applied to produce a joint as in the case of bookbinding or lamination; missing information in the case of thermal transfer printing. It has been shown that certain functionalized silicone fuser oils exhibit these problems to a greater extent than other release oils.
A number of patents have proposed solutions to these end-use application problems, such as U.S. patent Ser. Nos. 11/468,620; 11/623,509; 11/623,640; 11/850,138; 11/696,954; 11/743,447; 11/877,319; 12/016,524; 12/263,258; and 11/532,704, all of which are hereby incorporated by reference in their entireties. These references involve a modification of the adhesive or coating material to improve wetting and adhesion over oil contaminated prints or the inclusion of an additional coating to act as a coupling or tie-coat layer; consequently, these solutions are application specific. By contrast, the invention proposed here acts directly on the oil contaminated print surface to increase surface energy, resulting in significantly improved wetting adhesion potentially for all end-use applications which is seen as an advantage among available solutions.